1. Field of the Invention
This invention pertains to a variable geometry inlet for supersonic aircraft or missiles which uses a vented cowl.
2. Description of the Prior Art
One example of a vented inlet for subsonic and supersonic aircraft is disclosed in Goldsmith U.S. Pat. No. 3,524,458 of Aug. 18, 1970 where a bluff wall is disposed to move across the inlet to deflect the boundary layer so a portion of the airflow will move through a bleed aperture to the exterior.
An example of a movable cowl for a variable throat is seen in Moorehead U.S. Pat. No. 3,242,671 of Mar. 29, 1966 for the purpose of varying the cross-sectional area of the inlet throat for an airbreathing engine of supersonic character to reduce drag and obtain maximum airflow.
The patent of Larson U.S. Pat. No. 3,208,383 of Sept. 28, 1965 discloses a ramjet vehicle with a system of vents used with a circumferential air inlet for obtaining aerodynamic control when attached to the booster.
It is generally known that the performance of an air inlet for a supersonic aircraft or missile is related to its air mass capture and compression characteristics. The optimum manner of operation of an air inlet must capture the correct amount of air, must remain started at all times, and provide the proper airflow contraction characteristic to achieve the highest total pressure for the engine. The performance is degraded if there is too little or too much air, and an unstarted inlet causes excessive pressure losses because of a shock ahead of the inlet, air spillage and cowl drag.
The problem with the prior art is that none has the ability to vary the inlet capture and its contraction to achieve the degree of variability necessary for optimum or near optimum inlet performance for many vehicle applications. Many fixed geometry inlets are intended to be unstarted at the low velocity conditions (below the velocity where a ramjet will predominately operate), which causes substantial performance losses, in order to have higher contraction and higher performance at the high velocity ramjet flight conditions. This trading of losses for gains can be circumvented by the vented cowl inlet arrangement, as will appear hereinafter. Another problem exists with starting inlets having the required internal contraction for high performance at a given Mach number in that such an inlet has excessive internal contraction for starting and will not self-start.